Patch recordings from the electrocytes of electrophorus. Na channel gating currents.

Shenkel, Scott; Bezanilla, Francisco

doi:10.1085/jgp.98.3.465

Cited by 13 publications

(7 citation statements)

References 38 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The change in dielectric coefficient inside the pore would produce a change in the capacitance of the membrane in which the pore and channel are embedded. The change in capacitance clearly would have many, if not all of the properties of gating current (2)(3)(4)(5)(6). Gating currents are known to be associated with the opening and closing of voltage dependent ionic channels.…”

mentioning

confidence: 99%

Bubbles, Gating, and Anesthetics in Ion Channels

Roth

Gillespie

Nonner

et al. 2008

Biophysical Journal

100

View full text Add to dashboard Cite

We suggest that bubbles are the bistable hydrophobic gates responsible for the on-off transitions of single channel currents. In this view, many types of channels gate by the same physical mechanism-dewetting by capillary evaporation-but different types of channels use different sensors to modulate hydrophobic properties of the channel wall and thereby trigger and control bubbles and gating. Spontaneous emptying of channels has been seen in many simulations. Because of the physics involved, such phase transitions are inherently sensitive, unstable threshold phenomena that are difficult to simulate reproducibly and thus convincingly. We present a thermodynamic analysis of a bubble gate using morphometric density functional theory of classical (not quantum) mechanics. Thermodynamic analysis of phase transitions is generally more reproducible and less sensitive to details than simulations. Anesthetic actions of inert gases-and their interactions with hydrostatic pressure (e.g., nitrogen narcosis)-can be easily understood by actions on bubbles. A general theory of gas anesthesia may involve bubbles in channels. Only experiments can show whether, or when, or which channels actually use bubbles as hydrophobic gates: direct observation of bubbles in channels is needed. Existing experiments show thin gas layers on hydrophobic surfaces in water and suggest that bubbles nearly exist in bulk water.

show abstract

mentioning

confidence: 99%

Bubbles, Gating, and Anesthetics in Ion Channels

Roth

Gillespie

Nonner

et al. 2008

Biophysical Journal

100

View full text Add to dashboard Cite

show abstract

“…The ion channel configuration of the innervated membrane extracted from the AP curve using this method appear in Table 1; other physiological parameters, including the channel rate constants and the ion transporter configuration of the non-innervated membrane, were analyzed and are reported in the supplementary information. In the model, the conductance of Na + channels on the innervated membrane was found to be 1.57×10 3 ps·μm −2 , equivalent to a channel density of≈143 channels·μm −2 , which falls between reported values of ≈100 channels·μm −2 12, 13 to≈500 channels·μm −2 13. The innervated membrane capacitance was found to be 12.1 μF·cm −2 , which has been experimentally reported as 15.6μF·cm −2 5; this high capacitance can be due to high local tortuosity or modification to the lipid5, 14.…”

mentioning

confidence: 76%

“…Many electrophysiological parameters for the natural electrocyte, such as the channel rate constants and densities, are unknown or span a broad range12, 13. We found accurate values for these parameters numerically by using a nonlinear least square difference method to match initial model results with the nuances of the rise and fall of AP in published electrocyte data5 (Fig.…”

mentioning

confidence: 84%

Designing artificial cells to harness the biological ion concentration gradient

2008

View full text Add to dashboard Cite

Cell membranes contain numerous nanoscale conductors in the form of ion channels and ion pumps [1][2][3][4] that work together to form ion concentration gradients across the membrane, which can be triggered to release an action potential (AP) 1,5 . We ask if artificial cells can be built to utilize ion transport as effectively as natural cells. Here we used the electrogenic cell (electrocyte) of an electric eel to model the formation of AP by tracking the conversion of ion concentration gradients into APs across the different nanoscale conductors. Using the parameters extracted from the model, we designed an artificial cell based on an optimized selection of conductors. The resulting cell is similar to the electrocyte but has higher power output density and greater energy conversion efficiency. We suggest methods for producing these artificial cells that have applications in powering medical implants and other tiny devices.The electrocyte in an electric eel (Electrophorus electricus) can generate potentials of about 600V 2,3,6 to stun prey and ward off predators (Fig. 1a). The transmembrane proteins in the electrocytes are asymmetrically distributed across two primary membranes, one innervated and the other non-innervated (Fig. 1b), and are separated by an insulating septa (wall). The non-innervated membrane has numerous sodium potassium ATPase pumps (Na + /K + ) and both K + and chloride (Cl − ) channels. The innervated membrane contains high densities of acetylcholine receptors (AChRs), voltage-gated Na+ channels (which are responsible for activating APs), voltage-gated K + channels (Kvs) 7 , inward rectifier K + channels (Kirs, which are ion channels that stop ion flow when the membrane is depolarized) 6 and leak channels.When the chemical agonist, acetylcholine (ACh), is released into the junction between the AChR and another nearby excitable cell (synapse), AChRs bind with ACh and become permeable to the cations, Na + and K + . This opens the AChRs and depolarizes the innervated membrane, raising the probability that voltage-gated Na + channels will open (Fig. 1c) 3,6,8 . Depolarization causes the normally negative innervated cell membrane potential to become positive with respect to the potential on the non-innervated membrane. With Na + flowing into the cell, the innervated membrane potential further increases, causing the opening of additional voltage-gated Na + channels. This cascade of AChRs opening large number of Na + channels results in AP formation on the innervated membrane. The Kir channels are closed during this stage, which speeds the increase of the membrane potential. The maximum innervated 5,6 . The non-innervated membrane potential remains at approximately −85mV due to ATPase, K + channel and Cl − activity 2,5,6 . After the peak of the AP, the innervated membrane is repolarized with the inactivation of Na + channels 8 and the opening of Kir and Kvs channels. Ion flux through leak channels further expedites the restoration of membrane potential to the resting state (−85mV). The ion ...

show abstract

“…In cloned rat brain II sodium channels, either in transfected mammalian cells (West et al, 1992) or in Xenopus oocytes coexpressed with the A, subunit (Isom et al, 1992), inactivation has been found to be fast and more complete. The sodium currents recorded in patches from Electrophorus electrocytes show complete inactivation even at very positive potentials (Shenkel and Bezanilla, 1991). In the squid, this is clearly not the case in the macroscopic currents, and, as will be demonstrated in the accompanying paper (Correa and Bezanilla, 1994), neither is it the case at the single-channel level.…”

Section: Discussionmentioning

confidence: 99%

Gating of the squid sodium channel at positive potentials. I. Macroscopic ionic and gating currents

Correa

Bezanilla

1994

Biophysical Journal

View full text Add to dashboard Cite

Macroscopic ionic sodium currents and gating currents were studied in voltage-clamped, dialyzed giant axons of the squid Loligo pealei under conditions of regular and inverse sodium gradients. Sodium currents showed regular kinetics but inactivation was incomplete, showing a maintained current for depolarizations lasting 18 ms. The ratio of the maintained current to the peak current increased with depolarization and it did not depend on the direction of the current flow or the sodium gradient. The time constant of inactivation was not affected by the sodium gradient. Double-pulse experiments allowed the separation of a normal inactivating component and a noninactivating component of the sodium currents. In gating current experiments, the results from double-pulse protocols showed that the charge was decreased by the prepulse and that the slow component of the 'on' gating current was preferentially depressed. As expected, charge immobilization was established faster at higher depolarizations than at low depolarizations, however, the amount of immobilized charge was unaffected by the pulse amplitude. This indicates that the incomplete sodium inactivation observed at high depolarizations is not the result of decreased charge immobilization; the maintained current must be due to a conductance that appears after normal charge immobilization and fast inactivation.

show abstract

Patch recordings from the electrocytes of electrophorus. Na channel gating currents.

Cited by 13 publications

References 38 publications

Bubbles, Gating, and Anesthetics in Ion Channels

Bubbles, Gating, and Anesthetics in Ion Channels

Designing artificial cells to harness the biological ion concentration gradient

Gating of the squid sodium channel at positive potentials. I. Macroscopic ionic and gating currents

Contact Info

Product

Resources

About